Patent GB-905384-A (GB)
Title: Ferroelectric storage device
IPC: G11C11/22
Filed: 1959-03-26
Abstract: 905,384. Ferro-electric storage devices. STANDARD TELEPHONES & CABLES Ltd. March 26, 1959 [April 2, 1958], No. 10589/59. Class 40 (9). [Also in Group XXXVI] A storage cell comprises a ferro-electric wafer having a first electrode on one face, and second and third electrodes on the other face, the third electrode being adjacent the second so that it can modify the electric field between the first and second electrodes and thereby inhibit polarization of the material which would otherwise occur. Figs. 2 and 3 show a wafer of ferroelectric material 2, such as barium titanate having the first electrode 3 on one face and the second and third electrodes 4 and 5 having interlaced portions on the opposite face. The material has a rectangular hysteresis loop and a voltage + E across the wafer is necessary for polarizing the material for storing the binary " 1," or- E for reading out when a greater output is obtained from cell storing binary " 1 " than from an unpolarized cell. Fig. 6 shows the electrode structure in which X corresponds to electrode 3 and Y and Z to electrodes 4 and 5. If, say, + E/2 volts is applied to electrode Y, -E/2 to electrode X and zero volts to Z, then a voltage E appears across the material sufficient to cause polarization; reversal of the voltages to apply - E, is used for reading out. If equal and opposite voltages are applied to electrodes Y and Z the electric field is as shown in Fig. 6; these voltages neutralize each other so that the voltage across the wafer is only equal to that applied to electrode X (i.e. - E/2) which is insufficient for polarization or reading out. In a modification, a conductive foil is applied to the surface of the ferro-electric material and a dielectric is disposed between the foil and electrodes Y and Z. This provides a planar equipotential surface instead of the scalloped formation which is shown in Fig. 6, when the Z electrode is biased in the opposite sense to that of the Y electrode. Fig. 9 shows a three-dimensional storage array consisting of an assembly of a plurality of ferro-electric slices 26, 27, 28 each bearing a plurality of storage cells as described above, arranged in columns and rows. The X electrodes of all the cells in each row on all the slices are connected together, as are the Y electrodes of all the cells in each column on all the slices, and also the Z electrodes of all the cells on each slice. Thus any particular cell can be selected by choice of the appropriate one of each of the series of X, Y, Z connectors. Fig. 8 shows a circuit suitable for applying the required voltages to the electrodes 3<SP>1</SP>, 4<SP>1</SP>, 5<SP>1</SP> of the cell by means of a plurality of voltage generators and switches, which may consist of pulse generators. In this arrangement electrode 3<SP>1</SP> (X) is connected through position " a " of switch 21 to generator 20 and then to earth via capacitor 23 and rectifier 25 from which the output is taken; in position " b " of the switch, generator 20 is removed from this circuit. Electrode 4<SP>1</SP> (Y) is connected in position " a " of switch 19 to generator 22 and in position " b " to generators 18 and 22 in series. Electrode 5<SP>1</SP> (Z) is connected in position " a " of switch 17 to generator 22, and in position " b " to generators 16 and 22 in series. The generators supply an E output of + - volts and the switches can be 2 set to provide a writing in voltage, reading out voltage or numerous settings in which neither writing in or reading out occurs.